Solifenacin succinate is commercially marketed as pharmaceutically active substance indicated for the treatment of overactive bladder with symptoms of urinary incontinence, urgency and high urinary frequency. Solifenacin succinate is acting as a selective antagonist to the M (3)-receptor. The chemical name of the Solifenacin is (1S)-(3R)-1-azabicyclo[2.2.2]Oct-3-yl-3,4-dihydro-1-phenyl-2(1H)-isoquinoline carboxylate of formula (I);

Solifenacin succinate is the international common denomination for butanedioic acid compounded with (1S)-(3R)-1-azabicyclo[2.2.2]oct-3-yl-3,4-dihydro-1-phenyl-2(1H)-isoquinolinecarboxylate (1:1), having an empirical formula of C23H26N202.C4H604 and the structure is represented in formula VI given below;

Solifenacin and its pharmaceutically acceptable salts are first reported in U.S. Pat. No. 6,017,927 (927'), which disclosed two synthetic routes “Route-A and Route-B” for the preparation of (1RS,3′RS)-Solifenacin and (1S,3′RS)-Solifenacin as shown in Scheme-1:

Both the routes have several drawbacks such as;    a) Use of hazardous and pyrophoric reagent, NaH, in the process which is very difficult to handle and thus makes the process unsafe to handle at industrial level. The use of strong agent NaH also leads to racemization of the products and thus suffers to provide enantiomerically pure Solifencin;    b) Use of ethylchloroformate to prepare ethylcarboxylate derivative in route A which is lachrymatory in nature;    c) Ethylcarboxylate derivative produces ethanol as a by-product during trans-esterification reaction in the subsequent reaction that interferes in nucleophilic attack against Solifenacin in the presence of a base and hence it is necessary to remove ethanol from the reaction mixture in the form of azeotrope with toluene or the like simultaneously while carrying out the reaction, so as to control the reaction;    d) Use of column chromatography for the purification of Solifenacin base, which makes the process industrially not feasible;    f) The reaction requires longer time for the completion and hence turn around time of the batch in production makes it less attractive.
International Patent Application No WO2005/075474 disclosed another synthetic route for the preparation of Solifenacin and Solifenacin succinate as shown in Scheme-2.

The above route does not overcome the problems associated with the process disclosed in 927' as the process described in this scheme also uses ethylchloroformate in the first step and produces ethanol as a by-product in the second step.
Yet another International Patent application no WO2005/105795A1 discloses an improved process for preparing Solifenacin as represented in Scheme-3, wherein leaving group (Lv) can be 1H-imidazole-1-yl, 2,5-dioxopyrrolidin-1-yloxy, 3-methyl-1H-imidazol-3-ium-1-yl or chloro and further condensation is carried out in the presence of sodium hydride as a base and a mixture of toluene and dimethylformamide or toluene alone as a reaction medium. The process described herein represents few draw backs such as, use of hazardous sodium hydride, use of chromatographic purifications, and use of moisture sensitive leaving groups (Lv) and hence handling of the reaction is difficult. Further the leaving groups used are expensive and thus making the process uneconomic.

Hence, there is need of efficient process for producing Solifenacin and its succinate salt which is safe to handle, industrially feasible, and economically viable.